We compared our standard method of data presentation in the operating room (i.e., using "front end" equipment) with a newly developed, computerized monitoring system called the data acquisition and display system. These two systems differed in that data presentation using the standard front-end equipment was scattered and poorly structured, whereas data obtained from the newly developed system were unified and integrated. To effect the comparison, we examined the "controllability" (i.e., the precision of control) by the anesthesiologist of hemodynamic variables: arterial systolic, mean, and diastolic pressures, mean pulmonary artery pressure, mean central venous pressure, and heart rate. Controllability was assumed to be an indictor of the quality of anesthesia. All perioperative data were stored every 15 seconds on a floppy disk, and these data were available for analysis. The controllability was quantified by calculating the surface area of the signal of a variable outside a defined control zone; the smaller this surface area, the greater the controllability. A Mann-Whitney-Wilcoxon statistical test was done to test whether the two different data presentation systems would result in different levels of controllability (the first zero hypothesis). A Kruskal-Wallis test was done to examine the "inter-anesthesiologist variability" between the two systems (the second zero hypothesis). Our data showed great variability. Looking for factors that might explain this, we found that if preoperative systolic blood pressure was greater than 160 mm Hg and diastolic pressure was greater than 95 mm Hg, hemodynamic variables fluctuated more widely. We could show no differences in controllability when the two systems were compared overall.(ABSTRACT TRUNCATED AT 250 WORDS)